Light source system



Dec. 25, 1962 w. E. GLENN, JR 3,070,638

LIGHT SOURCE SYSTEM Original Filed March 2, 1959 3 Sheets-Sheet l Inv ntWilliam .8. Glenn His Attorney.

Dec. 25, 1962 w. E. GLENN, JR 3,070,683

LIGHT SOURCE SYSTEM Original Filed March 2, 1959 3 Sheets-Sheet 2 nven'br': WIN/am liQ/enn, Jn;

His Attorney.

Dec. 25, 1962 w. E. GLENN, JR 3,070,688

LIGHT SOURCE SYSTEM Original Filed March 2, v1959 3 Sheets-Sheet 3Inventor: Wi/h'am .E.G/enn Jn',

His Attorney.

United States Patent 3,070,688 LiGl-IT SGURCE SYSTEM William E. Glenn,lira, Scotia, N.Y., assignor to General Electric Company, a corporatienof New York Griginal application Mar. 2, 1959, Ser. No. 796,450. Di-

vided and this application Dec. 14, 1960, Ser. No.

8 Claims. (Cl. 249-4135) The present invention relates to a light sourcesystem having particular advantages as used for projecting light as afunction of the parameters of a diffraction grating in a lightmodulating medium. This application is a division of my applicationSerial No. 796,450, filed March 2, 1959, entitled, Projection System.

There are many applications in which it is desired to produce a viewableimage that is a function of applied or received electrical signals.Since television is probably the most common application, the presentdiscussion will be directed toward television applications although itis to be realized that it is applicable as well to any application inwhich it is desired to obtain light as a function of applied electricalsignals. In most television receivers the light image is directly viewedfrom the source from which it is generated-the phosphor screen.Unfortunately, such an arrangement has limitations as regards size andlight intensity and thus efforts have been directed in recent yearstowards producing projection systems. In one especially suitableprojection system, a deformable light modulating medium is used. Theapplied television signals modulate an electron beam that is deflectedover the surface of the deformable light modulating medium. On thismedium, the electron beam produces closely spaced lines of electroncharge, the charge densities of which are a function of the televisionsignals, and which for monochrome television signals correspondpoint-bypoint with the light intensity of the televised scene. Theselines of charge, which are attracted to a conducting plane beneath thelight modulating medium, produce corresponding lines of depressiondeformations, the depths of which depend upon the charge densities. Thespacing of the lines of charge are made close enough that the resultinglines of deformations have spacings of the order of grating linespacings and in fact these deformations form a difiraction grating. Avery bright light source having a narrow dimension in the direction ofthe diffraction grating projects light either through or on the lightmodulating medium. When there are no diffraction grating lines in thelight modulating medium the light that is either transmitted through orreflected from the light modulating medium is masked by a light mask.However, when there is a diffraction grating it diflracts the light,deviating it, so that some of the light is incident on transparent areasin the light mask, the amount of light so incident being dependent uponthe depths of the diifraction grating lines. Since these depths are afunction of the amplitude of the applied television signals, the lighttransmitted by the light mask is a function of these signals.Consequently, when this transmitted light is focused on a projectionscreen it produces a viewable image of the televised scene.

The brightness of the projected picture depends upon the number andintensity of the light sources that are utilized, and thus a pluralityof light sources are usually desired. Since these light sources have tobe narrow in width, a very convenient way of obtaining them is by usinga relatively large single brilliant light source, the light from whichis cast on a light mask having narrow slits. The light transmitted bythese narrow slits forms the desired light sources.

Unfortunately, with the above arrangement only a rela- 3,070,688Patented Dec. 25, 1962 "ice tively small portion of the light from thelight source is cast on the light modulating medium. The utilized lightis that from the light source that is directly incident on the slits inthe light mask and that light that is reflected by a reflector from theback side of the light source onto the slits. With the prior reflectingarrangements, only a small portion of the light from the light source isincident on the slits.

Accordingly, an object of the present invention is to provide animproved light source system in which the light is used efliciently.

A further object is to provide an improved reflecting arrangement.

In some applications it is desired to produce light images of characterssuch as letters of the alphabet and numbers. Ithas been diflicult toproject these characters with prior type projection systems since thesesystems difiract light in only one directionorthogonal to the narrowdimension of the light source. And since these light sources have beenlinear, this means that the pro-.

jected light can be diffracted only in one direction while many of thedesired characters and numbers have lines extending in differentdirections, the light corresponding to which would have to be diffractedin many directions if a single grating line arrangement is used, and itis desirable to utilize a single grating line.

Thus, another object of the present invention is to provide an improvedlight system for a diifraction type projection system capable ofprojecting light in many directions.

These and other objects are achieved in a preferred embodiment of myinvention in which light from a single light source is focused by anellipsoidal mirror on a cylindrical mirror producing a curvedconcentration of light usable as a concentrated source. This light maybe cast on the surface of a deformable light modulating medium. Thediffraction gratings in the light modulating medium can difiract lightin any direction and thus the projection of images of characters andnumbers can be readily obtained.

The novel features believed to be characteristic of the presentinvention are set forth with particularity in the appended claims. Myinvention, itself, however, together with further objects and advantagesthereof may best be understood by reference to the following descriptiontaken in connection with the accompanying drawings in which:

FIG. 1 is a perspective illustration of a preferred embodiment of myinvention,

FIG. 2 is a side elevational view, partially in section of FIG. 5 is aperspective view of one type of electron gun that can be used with theembodiment of FIG. 4 for the formation of characters, and

FIG. 6 is an enlarged view of a character matrix for the electron gun ofFIG. 5.

In the embodiment of FIG. 1, a source 11 of white light, preferably aXenon-arc lamp, is positioned at one of the focal points of and on theplane of the outer edge of an ellipsoidal mirror 12, which has anopening 13 for the insertion of one of the connectors to the lightsource 11. Source 11 is also positioned at the center of a sphericalmirror 14 which directs light incident thereon back onto the lightsource 11 so that a maximum amount of light is directed to mirror 12. Atthe other focal point of mirror 12, there is a first light mask 15 whichhas an aperture 17 in the form of two half moons that diminish in widthto zero at the points of contact of the two half moons.

A cylindrical mirror 18 is provided for causing the light from mirror 12to have the shape of aperture 17 when this light is at the position ofmask 15. Due to this shape, most of the light is incident on aperture 17and very little of it is masked. Mask 15 only gives a sharp edge to thislight.

The cylindrical mirror 18 has a cross section in the form of two arcs oftwo equal diameter circles, each of which extends approximately 160, andwhich meet at two points that are adjacent the two points of zerothickness of aperture 17. It can be shown that the center of each arc ofcylinder 13 should be half way between the center of light mask 15 andthe center of the outermost portion of aperture 17. Mirror 18 extendsfrom approximately the position of mirror 14 to close to mask 15 suchthat it intercepts all of the light from mirror 12 directed towards thecenter of mask 15. The light transmitted by the two halves of aperture17 produces, in elfect, two light sources.

With this type of light source arrangement substantially all of thelight produced by source 11 passes through aperture 17. Substantiallythe only light lost is that passing through aperture 13 in mirror 12 andthrough the aperture in mirror 14. The lead (not shown) that has to bebrought over to the upper pole of source 11 creates only a very smallshadow. Almost all of the remainder light, which is by far the most ofthe light produced by source 11, is incident on aperture 17.

The high light etficiency is obtained by substantially surrounding thelight source 11 with reflecting surfaces. However, a hole in mirror12--aperture '13is required to do this. With this aperture in the middleof mirror 12, the light from light source 11, when imaged, would have adark spot at its center, were it not for mirror 18. But mirror 18 causesthe image of the light source 11 to be substantially uniformlyilluminated. This can be shown by drawing lines representing the pathsof the light rays. In other Words, the light passing through aperture 17appears to originate from a round, uniformly illuminated light source.

The light transmitted by aperture 17 is focused by a lens 19 on a lightmodulating medium 26*, a film of which is formed on a rotating,transparent disk 21. The object distance for this light is from lens 1?to the upper edge of mirror 12. The image distance is from lens -19 tothe backside of disk 21. After passing through lens 19 the light isreflected from an infrared transmitting dichroic mirror 23 which directsthe visible light through another lens system 24. Lens system 24, in theabsence of a diffraction grating in the light modulating medium 20,focuses the light on an opaque region 26 of a second light mask 25 thathas transparent regions 27. Lens system 24, being very close to thelight modulating medium 20, does not appreciably affect the focusingaction of lens 19. The object distance for this light is from lens 24 tomask 15. The image distance is from lens 24 to light mask 25.

The light modulating medium is a transparent, deformable substance suchas, for example, one of those described in my copending application,S.N. 708,528, filed January 13, 1958, and assigned to the assignee ofthe present invention. A pool of this medium is held within a containerhaving a first section 29 and a second section 30 interconnected by afilter, not shown. As the disk 21 rotates in this medium, it is coatedwith a film onto which the diffraction gratings are formed. Since thisfilm is subjected to an electron beam it tends to cross-link to somedegree and thus a doctor blade 32 is provided for scraping off a portionof film into the container 30. A filter (not shown) between sections 29and 30 then filters out any cross-linked material that may be present.

Disk 21 must have a transparent conducting coating on one side, whichside is preferably the side on which the light exits from disk 21. Thetransparent conducting coating may be formed from many differentmaterials,

but it has been found that chrome or tin oxide is especially suitable.

Disk 21 is rotated through gears 33 by a motor 35 at a speed of theorder of 1 to revolutions per minute. The speed of revolution is notcritical but it should be great enough to prevent a significant amountof crosslinking of the material 21 at any one time. The electron beammay deflect several times over the same material without significantlycross-linking it. However, after a certain number of times the materialwill begin to crosslink significantly and thus the disk 21 should rotatethis material out of the raster area of the electron beam before thiscondition has been reached. The speed of rotation should not be so greatthat the diifraction grating in moving causes a smear of the picture. Atthe slow revolutions indicated, this will not occur.

A diffraction grating is formed in the light modulating medium 20 by anelectron beam 36 emanating from elec tron gun 37. Since the electron gunmay be one disclosed in the prior art, its details are not presented.

The electron beam 36 must, of course, pass through a highly evacuatedregion. This high vacuum is provided by a vacuum enclosure 39, onlypartially illustrated, to which there is connected a gas exhaust tube 40that is connected to a vacuum pump 42.

When there are dillraction gratings in the light modulating medium 20they ditfract the light so that some of it, the amount depending uponthe parameters of the diffraction grating, is transmitted through thetransparent areas 27 of the second light mask. The light so transmittedis focused by projection lens 44 on a projection screen 45. The objectdistance for this light is from lens 44 to disk 21. The image distanceis from lens 44 to screen 45.

In FIG. 2 there is illustrated a side view of the system of FIG. 1. Thelight source is housed in an enclosure 47 having heat vents 49 at topand bottom. At the top there is a heat cap 50 for absorbing the infraredradiation passing through dichroic mirror 23. If desired, a blowerarrangement may be provided for flowing cooling air through enclosure47.

The light modulating medium 20 and the rotating disk 21 are positionedwithin an evacuated enclosure 51 to which is connected the envelope 39for the electron gun.

The details of the enclosure 51 can be better seen in FIG. 3. Enclosure51 comprises a front wall 53, a back wall 54 and an intermediatecylindrical wall 55 that are maintained in fixed relationship by one ormore bolts 56. All of these parts are made separable because,eventually, the medium 20 may cross-link to such a degree that it has tobe replaced. Then, the enclosure 51 must be opened for the replacementof this medium. A side view is illustrated of the filter 57 that filtersout the cross-linked material. The container comprising sections 29 and30 is held in place by a bolt 59.

In the operation of the embodiment of FIG. 1, the light from lightsource 11 is formed into essentially two light sources by the action ofmirrors 12 and 18 and the light mask 15. One of these sources can beconsidered the light passing through the one half of aperture 17 and theother light source that light passing through the other half of aperture17. These light sources have a narrow dimension and are generallylongitudinally arranged, although they are curved. With the arrangementin FIG. 1, almost all of the light from light source 11 is utilized dueto the mirror arrangement. The presence of the mirror 18 prevents theformation of a hole in the middle of the light source that wouldotherwise be produced by the presence of the aperture 13 in mirror 12.With the shown arrangement, the light passing through aperture 17appears to come from a round, uniformly illuminated, light source.

The light passing through aperture 17 is incident upon the lightmodulating medium 20. If there are no diffraction gratings in lightmodulating medium 20, the light is completely masked by the opaque area26 of the second light mask upon which the light is focused by lens 24.If there are diffraction gratings having grating lines extending in adirection orthogonal to the widths of aperture 17 and of the maskingareas 26, they diifract light such that it is deviated from the opaqueregions 26 and is transmitted through the transparent areas 2.7.

The amplitude of the light so transmitted is a function of the amplitudeof the diffraction grating lines in the light modulating medium 20. Thistransmitted light is then focused by a projection lens 44 on aprojection screen 45. If the diffraction grating corresponds to atelevised scene, then the light transmitted by the second light mask andfocused on the projection screen 45 produces a black and white image ofthe televised scene.

As regards the advantages of this system of FIG. 1, one of the mostimportant advantages is that the image on screen 45 is, for the samesize light source, much brighter than that obtainable with priorprojection systerns. Also, since the light transmitted by aperture 17has the general shape of a circle there is no need for the use of ananastigmatic lens as with the prior projection system. That is, there isno appreciable astigmatism.

In FIG. 4, there is illustrated an embodiment of my invention in whichthe light can be diffracted in any direction through an angle of 360.This apparatus is very similar to that shown in FIG. 1 except for thefirst and second light masks, the cylinder 18 and the reflector 14. Onlythese different elements will be discussed.

In FIG. 4 the aperture 17 in the first light mask is an annular opening.To provide an annular ring of light on this opening 17 a cylinder 19having a circular cross section must be provided. Then the light fromthe ellipsoidal mirror 12 is in the form of an annular ring at theposition of the first light mask which serves merely to provide a sharpedge to this light ring- In FIG. 1 a spherical mirror 14 was placedabove the light source. This arrangement can as well be used in theembodiment of FIG. 4. However,- the illustrated arrangement is alsosuitable. In this arrangement the light source 11 is positioned near thebottom edge of the aperture 13 in mirror 12. The bottom edge ispositioned such that, preferably, a line drawn from it to the source 11makes an angle of approximately 20 with a plane that passes throughsource 11 and that is orthogonal to the axis of mirror 12. Mirror 12 iscurved such that its focal point is at source 11. With this arrangement,the spherical mirror 14 is placed below mirror 12 for reflecting thelight emanating from the lower half of thelight source 11 back ontosource 11. Thus, with this arrangement most of the light from lightsource 11 is utilized as it was in the light arrangement of FIG. 1embodiment.

Since the aperture 17 is now an annular ring, the opaque region 26 inthe second light mask 25 must likewise be an annular ring to mask thelight when there are no diffraction gratings in medium 20. When there isa diffraction grating it diffracts some of the light through thetransparent regions 27 of the second light mask.

Since there is annular symmetry to the optical arrangement in FIG. 4,light can be diffracted in any direction through an angle of 360. Thisis especially desirable in those applications in which the diffractiongratings extend in more than one direction.

In FIG. 5 there is illustrated an electron gun for providing an electroncharge pattern on the light modulating medium 20 corresponding tocharacters. This electron gun comprises a cathode and acceleratingstructure 60 for producing and accelerating an electron beam. This beamis directed by a deflection means 61 to the desired point on a charactermatrix 62, an enlarged view of which is illustrated in FIG. 6. Thecharacter matrix comprises an electron opaque piece of material 63 inwhich there are slits 64 in the form of the desired characters. When theelectron beam is directed through one of these slits, it obtains theshape of these slits. Thus, if the deflection means 61 directs theelectron beam, say to the character A, then the electron beam in passingthrough the slit A obtains the shape of the letter A. After the electronbeam has been directed to the desired character it is redirected to theaxis of the electron gun by a deflection system 65 illustrated as anelectromagnetic sys tem. Then the electron beam is directed to thedesired portion of the target area by a deflection system 67. If thetarget area is a phospor screen, the electron beam, since it is in theshape of a letter A, forms a letter A of light on the phosphor screen.By sequentially obtaining ditferent characters and properly positioningthem on the phosphor screen, a message can be written out.

In the illustrated apparatus a phosphor screen is not used but thefunction is the same. That is, the electron beam in the shape of thecharacter strikes the deformable medium, thereby producing an electroncharge pattern in the shape of this character. This pattern is thenattracted to the conducting coating on the disk 21 and in so beingattracted forms a depression in the shape of the letter that phasedilfracts the incident light through the transparent areas 27 of thesecond light mask such that the light when focused on the projectionscreen has the shape of the character. Due to the annular optics thedeformations in the light modulating medium can extend in any directionand yet the desired diffraction is obtained. It is also noted that thelines of the characters are formed by single lines that may extend atangles with respect to one another. In the prior projection systems eachcharacter line has to be formed from a plurality of parallel diffractiongrating lines. Thus, in these prior systems, a simple character matrix,such as is illustrated in FIG. 6, cannot be used in such prior system.

This system has the advantage of being very efficient in the utilizationof the light as has been mentioned with reference to the embodiment ofFIG. 1.

While the invention has been described with respect to certain specificembodiments, it will be appreciated that many modifications and changesmay be made by those skilled in the art without departing from thespirit of the invention. I intend, therefore, by the appended claims, tocover all such modifications and changes as fall within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A light system comprising an ellipsoidal mirror having an annularshape and having an aperture in its center, said ellipsoidal mirrorhaving an inner edge at the position of said aperture and an outer edge,said ellipsoidal mirror being curved such that said outer edge is in theplane of one focal point of said mirror nearer said inner edge, a lightsource positioned at said one focal point and having an input leadextending through said aperture, and a cylindrical mirror positionedcoaxial with said ellipsoidal mirror and extending such thatsubstantially all of the light from said ellipsoidal mirror directedtowards the other focal point of said ellipsoidal mirror is interceptedby said cylindrical mirror to produce an arcuate image in the plane ofthe last mentioned focal point.

2. The light system as defined in claim 1 in combination with aspherical mirror positioned between said light source and saidcylindrical mirror for reflecting substantially all of the lightincident thereon back onto said light source.

3. A light system comprising an ellipsoidal mirror having an annularshape and having an aperture in its center, said ellipsoidal mirrorhaving an inner edge at the position of said aperture, said ellipsoidalmirror being curved such that said inner edge is displaced of the orderof 20 from the plane of one focal point of said mirror, :21 light sourcepositioned at said one focal point and having an input lead extendingthrough said aperture, and a cylindrical mirror positioned coaxial withsaid ellipsoidal mirror and extending such that substantially all of thelight from said ellipsoidal mirror directed towards the other focalpoint of said ellipsoidal mirror is intercepted by said cylindricalmirror producing diverging light rays forming a focused arcuate image inthe plane of said other focal point.

4. The light system as defined in claim 3 in combination with aspherical mirror positioned beneath said ellipsoidal mirror at theaperture thereof for reflecting substantially all of the light incidentthereon back onto said light source.

5. A light system comprising an ellipsoidal mirror, a light sourcepositioned at one focal point of said ellipsoidal mirror, and acylindrical mirror positioned coaxial with said ellipsoidal mirror andextending along the ellipsoid major axis such that substantially all ofthe light from said ellipsoidal mirror directed towards the other focalpoint of said ellipsoidal mirror is intercepted by said cylindricalmirror to produce a distinct arcuate image in the plane of said otherfocal point formed of diverging light rays appearing to originate from auniformly illuminated source.

6. The light system as defined in claim 5 and a spherical mirrorpositioned to refiect substantially all of the light from said lightsource directed away from said ellipsoidal mirror back onto said lightsource.

7. A light system comprising a light source, a mirror arrangement aroundsaid light source for imaging the light from said source including afirst mirror means for bringing light from said source to a focus and acylindrical second mirror, coaxial with said first mirror means, forintercepting and reflecting said light before it reaches said focus ofsaid first mirror means for establishing in the plane of said focus anarrowly restricted elongated image, the light appearing to diverge froma uniformly illuminated source when viewed at said image being a largeportion of the light originating from said source.

8. A light system comprising ellipsoidal mirror, a light sourcepositioned at one focal point of said ellipsoidal mirror, and acylindrical mirror positioned coaxial with said ellipsoidal mirror andextending along the ellipsoid major axis such that substantially all thelight from said ellipsoidal mirror directed towards the other focalpoint of said ellipsoidal mirror is intercepted by said cylindricalmirror, said cylindrical mirror having a cross-section including pluralarcs of plural circles, the light intercepted by said cylindrical mirrorproducing an arcuate image in the shape of half moons in the plane ofsaid other focal point, formed of diverging light rays appearing to 1 toriginate from a uniformly illuminated source.

References Cited in the tile of this patent UNITED STATES PATENTS

